1. Field of the Invention
The present invention relates to a stereo image processing method and a stereo image processing apparatus.
2. Background Art
Standard stereo matching involves searching for a matching position using the similarity of an image feature amount including the value of luminance in a matching area. However, if the disparity changes significantly in the matching area, the similarity cannot be correctly determined due to the effect of a difference in distortion. This results in reduced matching accuracy. To suppress a decrease in matching accuracy, the matching area may be reduced so as not to contain a disparity variation. However, a smaller matching area is susceptible to noise and contributes to increasing the possibility of the presence of a similar pattern. This results in the increased likelihood of mismatching. Thus, to increase the matching accuracy, the matching area is desirably formed to be as large as possible so as not to contain a significant disparity variation. As a method for achieving this, JP Patent Publication (Kokai) No. 5-256613 A (1993) discloses a method including calculating the disparity for each pixel using matching windows of different sizes, and employing a processing result obtained using a matching window having the best reliability; the reliability is an index indicative of validity of a matching window size calculated based on the continuity of the disparity. That is, JP Patent Publication (Kokai) No. 5-256613 A (1993) discloses a method of adaptively varying the size of the matching area on a pixel basis.
Furthermore, JP Patent Publication (Kokai) No. 10-283474 A (1998) discloses a depth information extracting apparatus and a depth information extracting method in which the progressively reduced size of the matching window is applied, in order to improve the matching accuracy.
However, JP Patent Publication (Kokai) No. 5-256613 A (1993) improves the matching accuracy but disadvantageously requires high calculation costs. Furthermore, like JP Patent Publication (Kokai) No. 5-256613 A (1993), JP Patent Publication (Kokai) No. 10-283474 A (1998) improves the matching accuracy but disadvantageously requires high calculation costs, because of the need for disparity calculations executed on each pixel using a plurality of matching windows.
An object of the present invention is to improve both the matching accuracy and speed of stereo matching based on area matching, with reduced calculation costs.